1. Field of the Invention
This invention generally relates to a land disposal site for nuclear wastes having a non-structural cap supported by a solidly packed array of waste-containing modules which are arranged to be flexibly conformable with changes in the shape of the site brought about by seismic events or other natural disturbances.
2. Description of the Prior Art
Burial systems for burying nuclear waste are known in the prior art. In the earliest of these systems, such wastes were merely packed into 55-gallon steel drums, dropped into a simple, earthen trench by a long-boom crane, and buried. Unfortunately, such "kick and roll" burial systems proved to be generally unsatisfactory for the land disposal of nuclear waste. The loose soil which these trenches were filled in was much more permeable to water than the densely-packed soil which formed the sides of the trench, or the dense rock strata which typically formed the bottom of the trench. Consequently, the relatively loose and water permeable soil which surrounded the drums caused these trenches to collect large amounts of standing water in what is known as the "bathtub effect". This standing water ultimately caused the steel walls of the drums buried within the trenches to corrode and collapse. The collapsing drums and compaction of the soil over time resulted in a downward movement or subsidence of the soil, which caused a depression to form over the top of the trench. This depression in turn collected surface water and hence worsened the tendency of the trench to collect and maintain a pool of standing water over the drums. The resulting increase in standing water resulted in still more soil subsidence and accelerated the corrosion and collapse of the drums buried therein. The corrosion and collapse of the drum containers in such sites resulted in some radioactive contamination of the ground water flowing therethrough.
To solve the soil subsidence and water accumulation problems associated with such "kick and roll" disposal sites, a variety of alternative burial systems have been developed. These alternatives include earthen vaults having structurally rigid walls, and container burial sites which the spaces between the waste containers are filled in with concrete or some other hardenable grout. While these alternative systems constitute clear advances over the trenches used in the simple "kick and roll" disposal systems, various shortcomings are associated with both. For example, where earthen vaults are used which incorporate structurally rigid walls, such rigid walls are apt to crack and break in response to a seismic disturbance. Once the integrity of the vault walls is gone, ground water can flow in and accumulate around the waste packages. If any of these packages has metallic walls, the standing water surrounding them can cause the walls to corrode and leach radioactive waste into the ground water. Because such vaults typically have only one access opening, the recoverability of a single, leaking package would be extremely difficult, if not impossible. While burial sites in which a hardenable substance is poured over a large group of waste containers to form a solid, integral monolith may be more resistant to cracking or breakage due to seismic disturbances, this particular type of disposal site would tend to place very high, localized stresses on the waste containers located in the paths of any faults or cracks which develop in the monolith. Moreover, this type of site has an even worse problem with recoverability when a seismic disturbance does succeed in rupturing only a few or one of the containers encapsulated in the grout. A relocation of the site might be the only solution if such a cracking or breaking of the inaccessible containers occurred.
Clearly, a need exists for a disposal site which is structurally stable, yet flexible conformable to seismic events or other natural disturbances, so that no localized, container-cracking stresses can occur. Additionally, it would be desirable if the individual containers buried in such a site were easily and conveniently recoverable in order to obviate relocating the entire site should a seismic event or other natural disturbance break a few or only one of the containers buried therein. Further, the burial site should have means for preventing the accumulation of standing water around the array of containers to insure the longevity of the containers buried therein. Finally, it would be desirable if such a site were easily constructed of inexpensive materials.